Suspended Scattering Particles in Motion: A Novel Feature of OCT Angiography in Exudative Maculopathies

Kashani, Amir H.; Green, Kyle M.; Kwon, Julie; Chu, Zhongdi; Zhang, Qinqin; Wang, Ruikang K.; Garrity, Sean; Sarraf, David; Rebhun, Carl B.; Waheed, Nadia K.; Schaal, Karen Beate; Munk, Marion; Gattoussi, Sarra; Freund, K. Bailey; Zheng, Fang; Liu, Guanghui; Rosenfeld, Philip J. (2018). Suspended Scattering Particles in Motion: A Novel Feature of OCT Angiography in Exudative Maculopathies. Ophthalmology retina, 2(7), pp. 694-702. Elsevier 10.1016/j.oret.2017.11.004

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Objective: To characterize features of extravascular OCT angiography (OCTA) signals corresponding to hyperreflective intraretinal fluid across various exudative maculopathies.
Design: Multicenter, retrospective, observational study.
Participants: Patients whose eyes had various forms of exudative maculopathy, including diabetic retinopathy (DR), retinal vein occlusion (RVO), and neovascular age-related macular degeneration (nvAMD).
Methods: Patients with extravascular OCTA signal identified on en face OCTA images were included in this study. This signal was readily distinguishable from projection artifacts. The regions with the extravascular motion signal on OCTA were named “suspended scattering particles in motion” (SSPiM). Depth-encoded, color en face OCTA images (3 mm × 3 mm) centered on the fovea and their corresponding structural OCT scans were used to quantify features of SSPiM and the corresponding hyperreflective fluid. Longitudinal data were collected when available.
Main Outcome Measures: Anatomic location, the association with hyperreflective material, changes in location and appearance of SSPiM over time, and replication of SSPiM OCTA signal in an in vitro phantom.
Results: Seventy-six eyes in 62 patients with various forms of exudative maculopathy were evaluated (60 eyes with DR, 9 eyes with RVO, and 5 eyes nvAMD, 1 eye with macroaneurysm, and 1 eye with radiation retinopathy). Intraretinal accumulations of fluid with increased OCT signal intensity corresponded to regions of SSPiM in several exudative maculopathies. An in vitro phantom model demonstrates that particulate matter in suspension can generate a similar OCTA signal. SSPiM showed an anatomic preference for vascular–avascular junctions. The hyperreflective fluid corresponding to SSPiM appeared more frequently in the Henle fiber layer (HFL) than the inner nuclear layer (INL) and was highly associated with hyperreflective material (HRM) found bordering the fluid. In 5 of 8 longitudinal cases, the resolution of SSPiM resulted in the formation of confluent HRM. Clinically, this appeared as hard exudate on funduscopic images.
Conclusions: Clinical data suggest that SSPiM is a novel imaging feature of retinal vascular diseases that was not appreciated before the use of OCTA. We characterized several novel features of SSPiM and demonstrated that at least in some cases it resolves with residual hard exudate.

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